Our long range goals are to identify the role of repair enzymes (endonuclease, DNA polymerase and polynucleotide ligase) in the pathogenesis of liver cancer. Our immediate goals are to study: (1) the properties of a mammalian repair endonuclease, which nicks carcinogen-bound DNA; (2) the modulation of the activity of the enzyme after partial hepatectomy and during liver carcinogenesis; and (3) the restriction imposed upon enzyme activity by the interaction of DNA with other macromolecules.